So called “solid ink” printing machines encompass various imaging devices, including printers and multi-function platforms, which offer many advantages over other types of document reproduction technologies, such as laser and aqueous inkjet approaches. These advantages often include higher document throughput (i.e., the number of documents reproduced over a unit of time), fewer mechanical components needed in the actual image transfer process, fewer consumables to replace, sharper images, and an eco-friendlier process.
A typical solid ink or phase-change ink imaging device includes an ink loader which receives and stages solid ink elements that remain in solid form at room temperatures. The ink stock can be refilled by a user by simply adding more ink as needed to the ink loader. Separate loader channels are used for the different colors. For example, only black solid ink is needed for monochrome printing, while solid ink colors of black, cyan, yellow and magenta are typically needed for color printing. Solid ink or phase change inks are provided in various solid forms, and more particularly as pellets or as ink sticks.
An ink melt unit melts the ink by raising the temperature of the ink sufficiently above its melting point. During a melting phase of operation, the solid ink element contacts a melt plate or heated surface of a melt unit and the ink is melted in that region. The melted ink is often retained in a melt reservoir, which is itself heated to keep the ink above its solidification temperature until a print operation is demanded. The liquefied ink is supplied to a single or group of print heads by gravity, pump action, or both. In accordance with the image to be reproduced, and under the control of a printer controller, a rotating print drum receives ink droplets representing the image pixels to be transferred to paper or other media. To facilitate the image transfer process, a pressure roller presses the media against the print drum, whereby the ink is transferred from the print drum to the media. The temperature of the ink can be carefully regulated so that the ink fully solidifies just after the image transfer.
In higher throughput systems, the melted ink is pressurized for high speed delivery to the printheads. The throughput of such machines is ultimately controlled by the ability to maintain a constant supply of liquefied ink at the ready for delivery to the printheads. This ability is determined in part by the melt rate, i.e., the amount of solid ink that can be melted per unit time. In a typical ink stick system, the melt rates can vary between 6 and 16 gm/min. Higher melt rates can be often be achieved using solid ink pellets stored in a drum and fed to a high efficiency, high wattage melter. One such high volume melter is disclosed in co-pending and commonly-owned U.S. patent application Ser. No. 12/638,863 (the '863 Application), filed on Dec. 15, 2009 and entitled “SOLID INK MELTER ASSEMBLY”, the disclosure of which is incorporated herein by reference in its entirety. Melters of this type can achieve melt rates of up to 250 gm/min with sufficient power to exceed the ink's heat of fusion and the latent energy required to raise the ink to the final setpoint temperature for moving to the printheads.
There remains a need for a system capable of delivering ink to the print heads at a rate that can take full advantage of these high melt rates.